In U.S. Pat. No. 4,736,101 there is disclosed a method for performing MS/MS in a quadrupole ion trap. In this method a wide range of ions are created and stored in the ion trap during an ionization step of the analysis in a manner similar to that disclosed in U.S. Pat. No. 4,540,884. All the masses below the parent mass of interest are eliminated from the ion trap by scanning the amplitude of the r.f. voltage applied to the ring electrode. At this point, the parent masses of interest and other ions having masses greater than the parent remain trapped in the device. According to the equations that govern operation of the device, ions of differing masses will have distinct and unique natural frequencies of oscillation in the ion trap. Particularly, ions can be excited by input ac voltages of appropriate frequency applied to the end caps of the ion trap. This causes the excited ions to increase in trajectory and kinetic energy in the z direction of the ion trap. All other ions which have different masses remain unaffected by this supplemental or excitation ac voltage. With the increase in their kinetic energies, the ions undergo collision with background neutral gas molecules or atoms and fragment to smaller ions known as daughter ions. This is called collision-induced dissociation (CID). After a period of time, the supplemental ac voltage is turned off. The trapped daughter ions are then scanned out of the device by ramping or increasing the r.f. voltage applied to the ring electrode as disclosed in U.S. Pat. No. 4,540,884. Only parent ions of a single mass are excited at any given time. For tandem mass spectrometry (MS/MS) this provides only daughter ion experiments, i.e., mass-selecting or mass-isolating a single parent ion and then resonantly exciting it to undergo collision-induced dissociation (CID) to produce the daughter ions which are scanned and detected.
It is possible to obtain a reconstructed parent ion spectrum from a large number of successive daughter ion scans, each with its own ionization event. The time involved in acquiring the entire data would prevent the use of this approach for obtaining parent ion information during continuous mixture analysis.
In tandem mass spectrometry, two very useful scan modes for screening analytical samples are the parent scan and the neutral loss scan. The parent scan is useful for screening for classes of compounds whose parent ions fragment to a common and characteristic daughter ion, e.g., most of the phthalates (M+H).sup.+ ions fragment upon collision-induced dissociation to form a characteristic 149.sup.+ ions. The neutral loss scan is used to screen for classes of compounds whose parent ions fragment upon CID to form daughter ions via loss of a common neutral fragment, e.g., the M.sup.+ and M.sup.- ions of chlorinated compounds often lose Cl or HCl upon CID to form daughter ions. These types of scan modes have not been implemented on quadrupole ion trap mass spectrometers. With the demonstrated high sensitivity of quadrupole ion traps, these scan modes should markedly broaden the analytical capabilities of quadrupole ion trap spectrometers.